1. Field of the Invention
The present invention relates to a plate-fin type heat exchanger which can be used as, for example, a radiator for cooling a cooling water of an internal combustion engine for a vehicle.
2. Description of Related Art
Conventionally, a plate-fin type heat exchanger described in JP-A-58-127092 has been known, for example. The plate-fin type heat exchanger includes a plurality of plate fins, a plurality of tubes penetrating through the plate fins, and upper and lower tanks disposed respectively at upper and lower two ends of the tubes. The plate fins are equipped with clearance holding portions for holding a clearance between each adjacent pair of plate fins (i.e., fin pinch) to a predetermined distance when the plurality of the plate fins are laminated.
FIGS. 4 through 6 show conventional type plate fins 100 having the tubes 101 penetrating through the plate fins 100, louvers 103 formed on the plate fins 100 and the clearance holding portions 105. As shown in FIG. 4, the tubes 101 are disposed in two parallel lines perpendicular to the flowing direction W of air as heat exchanging fluid, and the louvers 103 being cut to face toward the air flowing direction W are formed between each adjacent pair of tubes 101. The clearance holding portions 105 are respectively formed at a front edge side (an upstream side of the air flowing direction W), a rear edge side, and center positions of the plate fin 100 in the air flowing direction.
As shown in FIG. 5, the front line tubes 101 and the rear line tubes 101 are alternately formed with the louvers 103 in a longitudinal direction of the plate fin 100. Further, as shown in FIG. 6, each of the tubes has circular cross-section.
However, in the conventional plate-fin type heat exchanger shown in FIGS. 4 through 6, the clearance holding portions 105 are formed at the upstream side of the louvers 103 in the air flowing direction, and therefore, air flow is disturbed by the clearance holding portion 105 before air flows into the louvers 103. The louvers 103 are used for distributing air boundary layer caused when air passing through the clearances of the plate fins and for increasing the heat exchange efficiency. When the air flow is disturbed by the clearance holding portion 105 before air flows into the louvers 103, the louvers 103 cannot obtain sufficient effects. Further, because the clearance holding portions 105 are formed at upstream and downstream sides of the louvers 103 in the air flowing direction W, the louvers 103 cannot extend to edge portions of the plate fins 100. Thus, it is difficult to increase the number of louvers 103 for improving the heat exchange efficiency.